Ceramic process



T. G. M DOUGAL CERAMIC PROCESS April 24, 1&34.

Original Filed June 14, 1929 Patented Apr. 24, 1934 PATENT OFFICECERAMIC PROCESS:

Taine G: McDougal, Flint, Mich., assignor to A Spark Plug Company,Flint, Mich.,a company of Michigan Original application June 14, 1929,Serial No. 371,068. Divided and this application September 18, 1931,Serial No. 563,496. In Great Britain July 7, 1928 11 Claims.

This invention has to do with a new form of ceramic material for use inthe manufacture of ceramic wares and with the method of producing thatmaterial.

Crystalline aluminum silicates used in the ceramic industry haveheretofore been universally employed in the form of fully growncrystals, or fragments of fully grown crystals. It is in this form thatthey occur in nature. In the commercial or synthetic manufacture of suchsilicates for use in ceramic wares the raw material is fused and cooledat a slow rate, usually in the form of ingots of appreciable dimensions,and consequently the crystals are likewise fully grown.

When such crystalline material is used in the production of preformedceramic articles, it is essential that some binder be used to cause thecrystalline particles to adhere to each other for the crystalsthemselves are refractory and inca- 0 pable of cohering without completefusion or'solution by suitable fluxes at high temperatures.

Thus, in the manufacture of porcelains of high thermo-dielectricstrength and high resistance to heat shock, such as are used for sparkplug insulators and refractories, it is customary to employ as thenon-plastic ingredient aluminum silicates in the form of finelypulverized particles of fully grown crystals. Mullite (3A12Oz2SiOz)andalusite (A12O3Si02) sillimanite and other 0 very refractory aluminumsilicates high in alumina are the ones now generally used for thispurpose. To bind the particles together they are mixed with plasticmaterial, such as clay, with the addition of suitable fluxes eithercarried as 5 impurities by the plastic or non-plastic ingredients, orseparately supplied. From the resulting plastic workable mass theceramic wares are shaped, and these wares are then fired in the usualmanner. The firing is carried to a temperature sufficient to vitrify thewhole mass producing a bonded shape, but not to a high enoughtemperature to cause the bulk of the pulverized refractory crystals tobe softened or dissolved by the fluxes for the reason that to do sowould result in melting down the wares and causing them to lose theirshape. Owing to the insuflicient temperature the pulverized and stablecrystalline material consequently is substantially unaffected by thefinal firing. The crystals are held to- Q gether primarily by thewetting of their surfaces and by slight surface solution with the lessrefractory (fluxing) silicates present in the body. It has beenrecognized as desirable to improve the bond between the crystals andthereby also 5 improve the quality of the fired body by welding thecrystals into a crystalline framework, but, so far as I am aware, theonly method by which this result has been accomplished heretofore hasbeen by subjecting the ceramic composition to such ,high temperaturesthat practically complete fusion of all constitutents of the body tookplace with the result that molds had to be used to hold the ceramicmaterial and give it shape. It occured to me that if the crystallinealuminum silicates could be produced in amorphous or cryptocrystallinecondition, or in some other state of unstable crystallization, it mightbe possible to produce the desired crystalline framework within theshaped porcelain body by crystalline growth during final firing at theusual relatively low temperatures.

The crystalline aluminum silicates, such as mullite, are extremelyrefractory but it occurred to me that if they were subjected topractically complete'fusion and quickly cooled, and preferably subjectedto mechanical disintegration simultaneously with the cooling it would bepossible to obtain them in the desired state of unstablecrystallization. In carrying on this development in one experiment, asmall rod of a complex silicate consisting largely of mullite was heldin the flame of an oxy-acetylene blow torch, and the melted drops werecaught in a tank of water. It was thought that the sudden cooling of therefractory would prevent complete crystallization. However, uponexamination of the I cooled material, it was found to consist ofsubstantially fully grown crystals. This seemed to point to theimpossibility of accomplishing the result by the use of ordinary coolingmethods, but it occurred to me that the difficulty may have been thatthe blast force of the oxy-acetylene flame caused the particles ofmaterial to be broken off theparent rod before they had opportunity tocome to full liquid fusion. It also 9 seemed probable that the coolingmedium was not continuously in sufliciently intimate contact with thematerial to be cooled nor was a sufficiently large volume of the coolingmedium made use of to avoid crystallization. There was also lackinganyefiective mechanical comminution of the molten material.

It occurred to me that if the refractory material were heated toabsolute fusion and then poured drop by drop, or in'a very fine stream,into a trough down which a strong stream of water was flowing, it wouldbe possible to secure the desired result. In employing this method themolten material would be broken up by striking the trough and by theforce of the stream of water, into droplets, bubbles, sheets or ribbonsthat would present a maximum surface for contact with the coolingmedium. By employing a rapidly fiowing stream of large volume, theutmost comminution of the droplets as well as maximum and uniform rateof cooling would be assured.

In carrying out this conception it may, in some cases, be mostconvenient to direct a large stream of water under considerable pressureupon the thin stream of melted refractory so as to positively break upthe refractory into small particles, and effect thorough mixing with thecooling water. This may be done by employing a nozzle, such as used onfire hose, to direct the water on the thin stream of the moltenmaterial. The particles or globules of the material are carried on bythe stream into a tank where they settle out as'before. This fusing andrapid cooling treatment, the latter made possible by the smallness ofthe globules, rapidity of introduction into the cooling medium, and therapid fiow of the water, results in a product practically all of whichis in an unstable crystalline state. This unstable crystalline materialconsists of cryptocrystals, that is, crystals that require the highestmagnification to render them visible; of very minute crystals, thelargest of which are of magnitude of the order of .10 millimeters; andalso of unstable glass which latter crystallizes in the final firing ofthe product. In practically all aluminum silicate compositions producedby this process the majority of the crystals are very much under .10millimeters, and in some compositions practically no crystals areproduced of larger magnitude than .001 millimeters.

Porcelain batches were made up with the described material as thenon-plastic ingredient,

and articles were molded from the batch and fired in the usual manner.Examination of the fired bodies showed that there had been continued aswell as additional crystalline growth made possible because of thepresence of the unstable glass referred to above. The bodies, upontesting, proved to have increased mechanical and dielectric strength aswell as greater resistance to heat shock. I believe the better physicalproperties may be attributed to the growth of crystalline particles byaccretion from the unstable glass surrounding them, and by the joiningtogether of adjacent crystalline particles to form the fully developedstable crystals.

In the drawing I have illustrated diagrammatically several differentforms of apparatus by which my method may be carried out.

In Figure 1, the material which it is desired to produce in unstablecrystalline state is heated in a pot or crucible 10 by means of an arcpassing between electrodes 12 and 14 immersed in the pot. ,Any desirednumber of electrodes may be used. When, the refractory material hasreached the state of complete fusion, it is poured in a fine stream, ordrop by drop, into a stream of water flowing down a trough 16 anddischarging into tank 18. The melted material upon striking the troughis broken up into small droplets, and'is very rapidly and evenly cooledbecause of the large surface area exposed and the intimate contact withthe large volume of water.

Figure 2 shows a modified form of apparatus. Here the stream of moltenmaterial is broken up by a water jet under high pressure. The jet may beprojected from a fire hose such as shown at 22. The violence of theimpact of the jet of water on the molten material will break it up intofine particles or droplets and the large volume of water employed willassure rapid and even cooling. The jet discharges into a tank 18 wherethe material will settle out.

The above apparatus is diagrammatically illustrated and is capable ofgreat variation in practice. Other heating arrangements may be employedand the cooling means may be considerably varied so long as theessential step of very rapid cooling of the, molten material isretained.

The above process-is applicable to various kinds of refractorymaterials, but it is particularly valuable in the case of aluminumsilicates such as sillimanite, mullite and andalusite, and others of theclass of aluminum silicates having a higher alumina to silica molecularratio than kaolin. In applying the process to these aluminum silicates,I have preferably used with them a certain proportion of suitablefluxes. Where a single flux is employed I prefer to use it in theapproximate percentage indicated in the table below:

If desired, combinations of two or more fluxes may be employed. Theaddition of one of these aluminum silicates, in unstable crystallineform to a ceramic batch for use in making spark plug porcelains resultsin the production of a fired product possessing in much greater degreethe advantages of mechanical strength and resistance to heat stock. Asan example of one specific batch, I have had very good results withplugs made of av raw batch consisting of 50% plastic clay and theremainder non-plastic ingredients comprising 45% aluminum silicates, inunstable crystalline form and 5% magnesium oxide or other suitable flux.The specific non-plastic ingredient used was produced by the describedmethod from Durox, a commercial electric furnace product marketed by theVitrefrax Company of Los Angeles, California. In my copendingapplication, S. N. 291,127, filed July 7, 1928, I have claimed thismethod of making porcelain-like articles, both broadly and specifically,and have also claimed the resultant superior product.

Not only is my invention of value in the manufacture of the class ofporcelains such as are used for spark plug insulators, but also in themanufacture of all kinds of ceramic wares, both vitreous andnon-vitreous. Thus ceramic batches including as ingredients aluminumsilicates particularly those higher in alumina than clay, preparedaccording to my process, are well adapted for the manufacture ofrefractory linings for furnaces and various other heat resisting bodies.They are also obviously especially desirable in the manufacture of highgrade electrical insulators. It is possible to produce preformed waresfrom my improved material alone with the addition of suitable fiuxes,although in most cases, it will be found desirable to use a plasticbond.

I believe the great advantage of the unstable forms of the glass andcrystalline phases lies in the fact that upon firing further crystallinegrowth takes place. Where such highly refractory substances have beenemployed in the past in crystalline form, they were not completelyfused, and consequently did not amalgamate with the whole mass butappeared in the burned product in practically the same state in whichthey were introduced into the raw body. This may be explained asfollows:

Inasmuch as such ingredients are introduced in the raw ceramic batch asfinely ground and shattered fragments of their original crystallineforms, they do not have an opportunity (because they or theirderivatives are in a stable refractory and practically inert state) togrow by orientation into their natural full crystalline forms. Forinstance a raw ceramic batch into which fragments of refractoryandalusite crystals had been introduced would not develop in the firingprocess the formation of any of the desirable needle-like mullite(formerly erroneously identified as sillimanite) crystals because thelatter retain the shape and position of the andalusite fragments asintroduced.

By my invention the aluminum silicates are produced in an unstable formand are surrounded by material of nearly the same chemical compositionin amorphous and unstable state so that under subsequent heat treatment,as in the firing of the ceramic mass to form the final product, thearrested crystals grow by accretion from the surrounding material andthe unstable glass devitrifies to form additional crystalline shapes.

By my process the necessary ingredients to form normally grown crystals,such as the desirable needle-like mullite form, are introduced in anunstable form preferably with fluxes intimately included or in solution,and from the resultant product crystals easily form with application ofthe heat in the subsequent firing process. This resumed and additionalcrystallization during final firing produces the desired crystallinedistribution throughout the body giving the desired improvement in itsthermo-electric properties, mechanical strength, and resistance to heatshock.

The essential feature of my process is to cool the molten masses at asufficiently rapid rate to prevent or effectively prohibit or retardcrystalline growth such as would normally occur with such compositionsshould they be allowed to cool at normal or retarded rates such asprevail with the usual ingot process.

While I have indicated several methods by which my process may becarried out as well as a number of uses of the new product, it is to beunderstood that these are merely given as examples and do not indicatethe precise limits of the method or of the uses of the product.

This application is a division of my prior application, Serial No.371,068, filed June 14, 1929, said application being a continuation ofmy prior application, Serial No. 291,126 filed July '7, 1928.

I claim:

1. The method of producing aluminum silicates in the form ofcryptocrystals, minute crystals not exceeding .010 mm. in size, andunstable glass for use in the manufacture of ceramic shapes whichconsists in heating the material to fusion, dividing the material intosmall particles, and subjecting the particles to rapid cooling action.

2. The method of producing aluminum silicates in the form ofcryptocrystals, minute crystals not exceeding .010 mm. in size, andunstable glass for use in the manufacture of ceramic shapes whichconsists in heating the material to fusion, and subjecting it to contactwith a flowing stream of cooling liquid and simultaneously to mechanicaldisintegration.

3. The method of producing aluminum silicates in the form ofcryptocrystals, minute crystals not exceeding .010 mm. in size, andunstable glass for use in the manufacture of ceramic shapes whichconsists in heating the material to fusion in the presence of one ormore fluxes, dividing the material into small particles, and subjectingthe particles to rapid cooling action.

4. The method of producing aluminum silicates in the form ofcryptocrystals, minute crystals not exceeding .010 mm. in size, andunstable glass for use in the manufacture of ceramic shapes whichconsists in heating the material to fusion in the presence of one ormore fluxes, and subjecting it to contact with a flowing stream ofcooling liquid and simultaneously to mechanical disintegration.

5. The method of producing aluminum silicates in the form ofcryptocrystals, minute crystals not exceeding .010 mm. in size, andunstable glass for use in the manufacture of ceramic shapes whichconsists in heating the material to fusion in the presence of one ormore fluxes, and spattering it by contact with an obstructing surfaceand subjecting it to cooling contact with a stream of liquid.

6. The method of producing aluminum silicates in the form ofcryptocrystals, minute crystals not exceeding .010 mm. in size, andunstable glass for use in the manufacture of ceramic shapes whichconsists in heating the material to fusion in thepresence of one or morefluxes, and pouring the melted material in a thin stream upon a surfaceover which a stream of cooling liquid is flowing, and collecting it in asuitable settling chamber.

7. The method of producing aluminum silicates in the form ofcryptocrystals, minute crystals not exceeding .010 mm. in size, andunstable glass for use in the manufacture of ceramic shapes whichconsists in heating the material to fusion in the presence of one ormore fluxes, and subjecting the material to rapid cooling action.

8. The process of preparing aluminum silicates for use in porcelains andthe like, which consists in fusing an aluminum silicate with a flux, theflux being in sufiicient quantity to produce a proportion of unstableglass, and subjecting the material to rapid cooling action, producing analuminum silicate in the form of cryptocrystals, minute crystals notexceeding .010 mm. in size, and unstable glass.

9. The process of preparing aluminum silicates for use in refractoryceramic bodies which consists in fusing an aluminum silicate having ahigher ratio of alumina and silica than kaolin with a flux, andsubjecting the material in comminuted form to rapid cooling actionthereby producing aluminum silicate in the form of cryptocrystals,minute crystals not exceeding .010 mm. in size and unstable glass.

10. The process of preparing mullite for use in refractory ceramicbodies which consists in fusing mullite with a flux, and subjecting thefused material in comminuted form to rapid cooling action therebyproducing mullite in the form of cryptocrystals, minute crystals notexceeding .010 mm. in size and unstable glass.

11. The method of producing aluminum'silicates of substantial amorphouscontent for use in the manufacture of ceramic shapes which consists inheating the material to fusion, dividing the material into smallparticles, and subjecting the particles to rapid cooling action.

TAINE G. MCDOUGAL.

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